Mulching types of rotary lawn mowers have recognized advantages compared to conventional lawn mowers. In mulching mowers, the cutting deck is essentially enclosed, except for the open bottom, by a depending skirt portion so that the mowed clippings of grass and other vegetation are not discharged generally horizontally through one side, as by conventional lawn mowers, but rather are cut into small pieces and eventually deposited on and into the lawn to become mulch. This, in effect, returns to the lawn, clippings of grass and other vegetation which have nutrients that would otherwise be lost from the lawn and should eventually be replaced or added. Further, the time consumed by the removal of bags filled with grass and other vegetation, which often eventually adds substantially to municipal landfills, is avoided by mulchers. Also avoided is the time and effort required for bagging, raking, and other cleanup operations so that the resulting saving of time and effort otherwise required for such operations is substantial. In addition, as indicated above, the cut particles are returned to the lawn where they decompose, returning nitrogen and moisture to the soil, as well as providing nutrients which fertilize the growing lawn.
Despite these advantages, mulchers have not been overly popular compared to conventional rotary lawn mowers. The primary reason is that conventional mulchers operate most efficiently when cutting only about one-third of the height of the grass, and, to be effective, the mowing and mulching operations proceed generally slower than mowing operations carried out by conventional rotary mowers. These problems are compounded when mulchers are used on wet grass. Moreover, homeowners and professional lawn care and maintenance services generally attempt to maintain schedules. But frequently, at the scheduled time for cutting a particular lawn, it may be too damp to be cut by a mulcher, whereas a conventional lawn mower may do an adequate job. Thus conventional mowers are preferred because they are more adaptable to varying lawn conditions than conventional mulchers and allow more manageable lawn care scheduling. Further, routine lawn care schedules may require that more than one-third of the height of the grass be trimmed due to interim weather conditions conducive to rapid growth of the lawn. Accordingly, there is a need for mulcher mowers which can be controlled so that they can be used to cut heavy wet grass and other vegetation of a like nature, as well as to cut more than one-third of the height of the grass whereby the mulcher operates, insofar as the operator is concerned, in much the same manner as a conventional rotary blade side or top discharge mower.
For effective fine mulching, it is considered that grass cuttings should be drawn into the blade housing and induced by the moving air caused by the rotation of the blades, to be moved more or less along a spiral path within a toroid defined by the rotating blade's housing, so that most of the grass clippings are cut at least twice, and, at the same time, are being moved downwardly to be received within the lawn at the same rate that they are being cut to prevent overload conditions. Perforations provided in the blade housing may assist to achieve the desired movement of air which carries the grass cuttings and the like within the cutter blade's housing while avoiding overloads. Further, it is known that a rotary lawn mower can, in effect, be converted into a mulcher by blocking its discharge opening either with a solid plate, or a plate having perforations therein. But apparatus involved for such conversions, in general, has to be installed on the mower to provide the desired type of operation and subsequently removed to return the mower to its original mode of operations. This conversion can prove time consuming and may be difficult to accomplish under field conditions unless the mower and the conversion gear are much cleaner than is usually the situation after use.